The present invention relates to an engine cooling system for an automobile.
As shown in FIG. 1, a conventional cooling system in an automobile engine has a thermostat housing B disposed in a coolant passage F between an upper outlet of water jackets A of an engine AE and an upper inlet of a radiator E. A lower outlet of the radiator E is connected to a lower inlet of water jackets A by a passage G through a water pump D. A small bypass passage C is disposed between the thermostat housing B and water pump D.
During engine warmup at the initial stage, since the engine is cold, a thermostat valve in the thermostat housing B is closed to cut off the flow of coolant through the radiator E. Coolant is circulated by water pump D through water jackets A, thermostat housing B, and small bypass C as indicated by arrows, so that the temperature of the coolant rapidly rises.
As shown in FIG. 2, when the engine reaches its normal operating temperature, and the temperature of the coolant reaches a predetermined opening temperature of the thermostat, the thermostat starts to open. Thus, a part of coolant flows from the thermostat housing B into the radiator E through the passage F and flows from top to bottom in the radiator E, and drawn into the water jackets A through the passage G by the water pump D together with the coolant from bypass passage C, as indicated by arrows.
In practice, however, the heat sensitivity of the thermostat is low, so that the temperature rising rate of the thermostat is slow compared with the temperature rising rate of the coolant. Under certain conditions, the thermostat does not open at the predetermined temperature. For example, the thermostat starts to open at a temperature which is higher by about 20.degree. C. than the predetermined temperature. In such a case, since the thermostat suddenly opens and the low temperature coolant flows from the radiator E into the water jackets A through the water pump D, the temperature of coolant is rapidly lowered by the radiator which causes the thermostat to close again. If the peak of the heat overshoot occurring in the initial opening period of thermostat and the surge of pressure occurring at the closing of the thermostat simultaneously occur and repeat, so that cracks of water jackets, cylinder head, breakdowns of the thermostat, radiator, and other problems will occur, this will cause serious engine troubles.